Butanol is an important industrial chemical with a variety of applications, such as use as a fuel additive, as a blend component to diesel fuel, as a feedstock chemical in the plastics industry, and as a foodgrade extractant in the food and flavor industry. Each year 10 to 12 billion pounds of butanol are produced by petrochemical means. As the need for butanol increases, interest in producing this chemical from renewable resources such as corn, sugar cane, or cellulosic feeds by fermentation is expanding.
In a fermentative process to produce butanol, in situ product removal advantageously reduces butanol inhibition of the microorganism and improves fermentation rates by controlling butanol concentrations in the fermentation broth. Technologies for in situ product removal include stripping, adsorption, pervaporation, membrane solvent extraction, and liquid-liquid extraction. In liquid-liquid extraction, an extractant is contacted with the fermentation broth to partition the butanol between the fermentation broth and the extractant phase. The butanol and the extractant are recovered by a separation process, for example by distillation.
J. J. Malinowski and A. J. Daugulis, AlChE Journal (1994), 40(9), 1459-1465, disclose experimental studies to assess the effect of salt addition on the extraction of 1-butanol, ethanol, and acetone from dilute aqueous solutions using cyclopentanol, n-valeraldehyde, tert-amyl alcohol, and Adol 85NF (comprised largely of oleyl alcohol) as extractants. The authors note in their conclusions that in spite of the advantages that salt addition offers to the extraction of ethanol, 1-butanol, and acetone from dilute aqueous solutions typically found in fermentation processes, the practical implementation of such a process configuration is presently limited. As an in situ recovery strategy (extractive fermentation) the relatively high salts concentrations which may be required could have severely deleterious effects on cells arising from osmotic shock.
Published Patent Application US 2009/0171129 A1 discloses methods for recovery of C3-C6 alcohols from dilute aqueous solutions, such as fermentation broths. The method includes increasing the activity of the C3-C6 alcohol in a portion of the aqueous solution to at least that of saturation of the C3-C6 alcohol in the portion. According to an embodiment of the invention, increasing the activity of the C3-C6 alcohol may comprise adding a hydrophilic solute to the aqueous solution. Sufficient hydrophilic solute is added to enable the formation of a second liquid phase, either solely by addition of the hydrophilic solute or in combination with other process steps. The added hydrophilic solute may be a salt, an amino acid, a water-soluble solvent, a sugar or combinations of those.
U.S. patent application Ser. No. 12/478,389 filed on Jun. 4, 2009, discloses methods for producing and recovering butanol from a fermentation broth, the methods comprising the step of contacting the fermentation broth with a water-immiscible organic extractant selected from the group consisting of C12 to C22 fatty alcohols, C12 to C22 fatty acids, esters of C12 to C22 fatty acids, C12 to C22 fatty aldehydes, and mixtures thereof, to form a two-phase mixture comprising an aqueous phase and a butanol-containing organic phase.
U.S. Provisional Patent Application Nos. 61/168,640; 61/168,642; and 61/168,645; filed concurrently on Apr. 13, 2009; and 61/231,697; 61/231,698; and 61/231,699; filed concurrently on Aug. 6, 2009, disclose methods for producing and recovering butanol from a fermentation medium, the methods comprising the step of contacting the fermentation medium with a water-immiscible organic extractant comprising a first solvent and a second solvent, the first solvent being selected from the group consisting of C12 to C22 fatty alcohols, C12 to C22 fatty acids, esters of C12 to C22 fatty acids, C12 to C22 fatty aldehydes, and mixtures thereof, and the second solvent being selected from the group consisting of C7 to C11 alcohols, C7 to C11carboxylic acids, esters of C7 to C11 carboxylic acids, C7 to C11 aldehydes, and mixtures thereof, to form a two-phase mixture comprising an aqueous phase and a butanol-containing organic phase.
Improved methods for producing and recovering butanol from a fermentation medium are continually sought. A process for in situ product removal of butanol in which electrolyte addition to a fermentation medium provides improved butanol extraction efficiency and acceptable biocompatibility with the microorganism is desired.